This invention relates to stabilization of conductive polymers and is especially directed to a method of stabilizing electrically conductive polymers, particularly polypyrrole or polyaniline, to hostile environments.
Conductive polymers, such as polypyrrole or polyaniline, can be prepared using either electrochemical or purely chemical means. Thus, polypyrrole is produced by electropolymerization as described by A. F. Diaz, et al in an article entitled "Electrochemical Polymerization of Pyrrole" in the Journal of Chemical Society, Chemical Communications, 1979, page 635. This process produces thin (from about 20 nm to 20 .mu.m) free-standing films. N-substituded analogs of pyrrole such as poly-N-methylpyrrole and poly-N-phenylpyrrole have been used to form polypyrrole as reported by A. F. Diaz, et al in an article entitled "Electrochemistry of Conducting Polypyrrole Films" in the Journal of Electroanalytical Chemistry, 129, (1981) pages 115-132. However, the resulting conductive polypyrrole does not have the bulk and ductility required to make the material useful in structural-related applications.
U.S. Pat. No. 4,552,927 to L. F. Warren discloses a conductive polypyrrole which can be produced in thicker layers and has increased mechanical flexibility as compared to prior art polypyrrole film, obtained by electropolymerizing pyrrole from an electrolyte containing a non-nucleophilic polymeric anion, such as polystyrene-sulfonate, and pyrrole.
U.S. Pat. No. 4,582,575 to L. F. Warren, D. S. Klivans and L. Maus discloses an electrically conductive composite comprising a dielectric porous substance, such as fiberglass fabric, and an electrically conductive pyrrole polymer deposited in the pores of such substance, by contacting such porous substance with an anode in an electrolytic cell containing an electrolyte comprising a pyrrole monomer and a substantially non-nucleophilic anion, such as sulfate, and electrochemically depositing a conductive pyrrole polymer in the pores of such substance.
U.S. Application Ser. No. 646,717, filed Sept. 4, 1984, of P. R. Newman, L. F. Warren, Jr. and E.F. Witucki, and assigned to the same assignee as the present application, now U.S. Pat. No. 4,617,228 discloses a chemical process for producing an electrically conductive composite which comprises contacting a dielectric porous substance, such as fiberglass fabric with a liquid pyrrole, contacting the porous substance with a solution of a strong oxidant capable of oxidizing pyrrole to a pyrrole polymer, such as ferric cation, and oxidizing the pyrrole in the presence of a substantially non-nucleophilic anion, such as sulfate, and precipitating a conductive pyrrole polymer in the pores of such substance.
A requirement for the conductive polymeric material prepared by any of the above methods is that the electrical properties remain stable in potentially hostile environments. Such environments include, for example, 250.degree. F. in air, 100% O.sub.2 at room temperature, and 90% relative humidity at 160.degree. F. In addition, these conductive materials should exhibit a long-term shelf life stability. It has been shown that in the neat or pure and unprotected state, these conductive polymeric compounds are not very stable in the above environments, and lose their electrical conductivity.